1. The Catholic University of America Aldo Glean ENGR 518 Experimental Techniques for Graduate Students December 04, 2012 Measurement Of the Acoustic Properties Of Materials (Absorption and Reflection Coefficients)

2. Outline  Description Measurement System (Impedance Tube)  Functionality of Measurement System  Measurement Results  Limitations of Measurement System

3. Impedance Tube Clear tube with cork dust

4. Impedance Tube Standing wave tube:  Measure Absorption and Reflection Coefficient of materials (single and multilayer)  Material use: Minimize reverberation in recording studios, interior of vehicles, classrooms & offices Excitation (speaker) Microphones Piston Sample

5. Impedance Tube  Microphones measure acoustic pressure at two locations in the tube (Transfer function method)  Complex Transfer Function (H): Mic #2 to Mic #1 Excitation signal

6. Impedance Tube  Measurement system parameters ( ASTM: E 1050-98 ) Restriction of higher modes Excitation signal

7. Impedance Tube  Overview of System in Operation Mic Power Supply Power Amplifier Computer with Digitizer Excitation signal

8. Impedance Tube  Measurement using Melamine Foam Sample cross-section: Cross-section of tube Thickness: Limited by depth of tube Speaker Microphones

9. Impedance Tube  Absorption and Reflection Coefficients Fig1: Absorption and Reflection coefficient of Melamine foam.

10. Impedance Tube  Measurement Limitations Measurements are made at Normal Incidence (compensation for other angles is possible) Upper frequency is limited by: Plane wave requirement (tube diameter) Microphone spacing

11. Questions?